The internet is awash with news that NASA's Curiosity Mars rover has detected carbon compounds on Mars. Some people may have you believe that the news suggests there's life on Mars—but don't get too excited just yet.

Carbon compounds...

One of Curiosity's main goals is to hunt out organics on Mars. These are carbon-based molecules that we take for granted on Earth, but which are the fundamental blocks from which carbon-based life forms are built. Finding them could suggest that life exits—or did exist—on Mars.

The news from NASA shows that, when soil was tested using Curiosity's onboard chemistry set, carbon, hydrogen and chlorine were present and capable of reacting with each other to form organic compounds. Tantalizing. Does that mean, then, that there's life on the planet?

...but no signs of life

Hold on a minute, though. An important point in this story is that the samples were tested in the onboard equipment of Curiosity. In fact, they're heated up in something akin to a miniature oven—and it's not clear whether the carbon found in the samples was actually from the surface of Mars, or simply residue in the device from back here on Earth.

Even, thinking positively for a moment, if the carbon was from the surface of Mars, it's not enough to suggest there was life on the planet, because the element could be present in inorganic sources, too, like carbonate rocks. If you need it from a more official source, then senior NASA scientist Paul Mahaffy spells it out quite clearly:

"We have no definitive detection of Martian organics at this point."

So, sure, organics are present on Mars. But that could be because NASA took them there, or because they were created from inorganic sources or maybe—and it's a very big maybe—they're a hangover from Martian life. Either way, NASA has no way of telling, so you shouldn't get too excited about it either. [NASA, New Scientist]